Boron-based fuels with auxiliary exothermic reactions for air-breathing ramjets
Abstract
Combustion of solid fuels is a highly coupled complex process involving multiphase compressible flows. Metallic particles are oftenadded to boost the energy density of the fuel further complicating the combustion process. The local contribution of the metallic particles to the energy balance at the fuel#s surface is limited by time and reactive species, thus parameters such as particle size and composition are important. As the subsurface of the fuel is heated due to conduction, convection, and radiation, particles are subjected to very high heating rates. After ejection from the fuel surface, particles pass through a boundary layer before being entrained in the core flow which is oxygen rich. The boundary layer in which the diffusion flame lies, is depleted of oxygen, and is expected to comprise fuel rich pyrolysis products, nitrogen, and products of the diffusion flame such as water vapor and carbon dioxide. Boron, while especially interesting for use in solid fuels due to its high gravimetric and volumetric heating value, is not particularly reactive with any of the expected species in near surface boundary layer. On the other hand, other metals such as aluminum, titanium, and magnesium to name a few, are relatively reactive to these gas phase species. If particles can begin to react exothermically in this region, they will contribute positively to the surface energy balance altering fuel regression rates and flameholding characteristics. Alternatively, particles could contribute to the energy balance if they are able to react exothermically in the subsurface or very near the surface with the aid of an additional catalytic or oxidative component. These effects lead to greater operating envelopes for solid fuel combustion.The overarching objective of this research is to understand, describe, and model the critical, rate-controlling physicochemical processes of composite powders which may be used as fuel supplements in solid fuels. Ideally the fundamental understanding leads to particles which can take specifically target combustion mechanisms in order to alter the near surface energy balance. Specific objectives include: #develop novel boron based composite powders which can lead to a greater understanding of target combustion mechanisms involving auxiliary exothermic reactions;#thoroughly characterize the composite powders including ignition times and combustion rates;#include the powders in a host polymer to formulate solid fuels that will be studied to determine the effect of the powders on the fuel surface energy balance. Composite powders will be develop using arrested reactive milling and studied experimentally individually and in solid fuels such that fundamental combustion mechanisms and general combustion behavior can be fully described. A computational model will also be developed to provide a means of probing combustion mechanisms and comparison to the experiments. The knowledge gained will enable the DoD to develop revolutionary solid fuels with wider operating envelopes. Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 24, 2024
- Source ID
- N000142412096
Entities
People
- Gregory Young
Organizations
- Office of Naval Research
- United States Navy
- Virginia Tech